Airbag, airbag device and vehicle

ABSTRACT

An airbag device includes an airbag and an inflator disposed at a side of a base portion of the airbag for inflating the airbag. The airbag includes a left half airbag with a vent hole to be inflated at a front left of a vehicle occupant, and a right half airbag with a vent hole to be inflated at a front right of the vehicle occupant. The distal ends of the left half airbag and the right half airbag are spaced part from each other to form an empty space therebetween facing the vehicle occupant when the airbag is inflated.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part application of patent application Ser.No. 10/671,801 filed on Sep. 29, 2003.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an airbag for protecting a vehicleoccupant in the event of vehicle collision, and specifically relates toan airbag having a left half airbag to be inflated at a front left ofthe occupant, and a right half airbag to be inflated at a front right ofthe occupant. The present invention also relates to an airbag deviceprovided with the airbag and a vehicle provided with the airbag device.

Japanese Patent Publication (KOKAI) No. 04-292239 has disclosed anairbag for protecting a vehicle occupant in the event of vehiclecollision. The airbag has a left half airbag to be inflated at a frontleft of the occupant, and a right half airbag to be inflated at thefront right of the occupant. A common inflator inflates both the lefthalf and right half airbags. In the airbag, a distal end of the lefthalf airbag is connected to a distal end of the right half airbag with atie panel.

The airbag is folded in a case and covered with a cover. In the event ofvehicle collision, an inflator, i.e. a gas generator, injects gas toinflate the airbag rapidly in front of the occupant by pushing andopening the cover.

The inflator is disposed at an inside or outside of a base portion ofthe airbag. In an airbag device having an inflator disposed at anoutside of the base portion of the airbag, the gas from the inflator issupplied into the airbag through a gas inlet disposed at the baseportion side of the airbag. In an airbag device having an inflatordisposed at an inside of the base portion side of the airbag, theinflator is entirely or partially disposed in the airbag. An example ofthe latter case includes a configuration in which a pair of slitopenings is formed in the airbag, and a rod inflator passes through theslit openings, so that both ends of the inflator expose at the outsideof the airbag.

As airbags for protecting vehicle occupants, there are a curtain airbagto be expanded along a side portion of a vehicle cabin (side door or Bpillar), a knee airbag to be expanded in front of a leg of an occupant,a side airbag to be expanded toward a side of an occupant, and a seatcushion airbag to be expanded at a lower front side of a seat cushion toleft or harden a front portion of the seat cushion. The seat cushion baglifts or hardens the front portion of the seat cushion to preventso-called submarine phenomena in which an occupant slides down under aseat belt in case of vehicle collision. Japanese Patent Publication(KOKAI) No. 2001-247010 has disclosed such a seat cushion airbag.

In the airbag disclosed in Japanese Patent Publication No. 04-292239,the distal ends of the left half and right half airbags are connectedwith the tie panel. Therefore, when the airbag is inflated, the tiepanel receives a center part of the vehicle occupant's body in thelateral direction. When the left half and right half airbags areinflated, a larger amount of the gas may flow in one of the half airbagsfrom the inflator, and then the other of the half airbags is inflatedlater than the one of the half airbags.

As described above, the distal ends of the left and right half airbagsare connected with the tie panel. Accordingly, it is expected that whenone of the half airbags is inflated faster than the other, the one ofthe half airbags may facilitate the other of the half airbags to beinflated by pulling the other of the half airbags through the tie panel.As described above, however, the tie panel connects the distal ends ofthe left and right half airbags. Therefore, the one of the half airbagsdoes not sufficiently pull the other of the half airbags through the tiepanel until the one of the half airbags is inflated up to the distalend.

In view of the problem described above, an object of the presentinvention is to provide an airbag wherein a left half airbag and a righthalf airbag are inflated smoothly and substantially uniformly towardleft and right sides from an early stage of the inflation.

Another object of the invention is to provide an airbag having a venthole at an appropriate position.

A further object of the invention is to provide an airbag deviceprovided with such an airbag and a vehicle provided with the airbagdevice.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

According to the present invention, an airbag device includes an airbagand an inflator disposed at a side of a base portion of the airbag forinflating the airbag. The airbag is inflated such that a distal endthereof extends away from the base side of the airbag. The airbagincludes a left half airbag to be inflated at a front left of a vehicleoccupant, and a right half airbag to be inflated at a front right of thevehicle occupant. The left half airbag has a distal end connected with adistal end of the right half airbag, and a space facing the vehicleoccupant is formed between the distal ends of the left and right halfairbags when the airbag is inflated.

In the invention, when the airbag is inflated, a distance between thedistal ends of the left and right half airbags may be 150 to 450 mm.Also, a distance from the distal ends to a deepest bottom of the spacemay be 280 to 480 mm.

According to the present invention, the left half airbag may beconnected with the right half airbag at base portions thereof surfaces,so that a common inflator inflates the left and right half airbags.

According to the present invention, the left half airbag may beconnected with the right half airbag at middle portions thereof in adirection that the airbag expands. When the airbag is inflated, adistance from the distal ends of the left and right half airbags to theconnected middle portions may be 50 to 300 mm. The left and right halfairbags are formed of a plurality of panels joined with each other. Thepanels are joined at joined portions at an outside of the middleportions of opposing surfaces of the half airbags.

According to the present invention, the airbag may include vent holes inouter side surfaces at upper front areas from middle portions of theside surfaces.

According to the present invention, an airbag device is provided withthe airbag of the invention and an inflator for inflating the airbag. Inthe airbag device, the airbag is inflated at a maximum pressure lessthan 440 kPa.

According to the present invention, a vehicle is provided with theairbag device. In the vehicle, the airbag device may be installed in aninstrumental panel of the vehicle as a passenger side airbag. A venthole is formed in a side surface of the airbag facing outwardly. Whenthe airbag is inflated, a horizontal distance L1 between a rear edge ofthe instrumental panel and the vent hole and a horizontal distance L2between the rear edge and the distal end of the airbag has a ratio(L2/L1) of 0.25 to 0.5. Also, when the airbag is inflated, a verticaldistance H1 between an upper edge of the instrumental panel and the venthole and a vertical distance H2 between the upper edge and the distalend of the airbag has a ratio (H2/H1) of 0.3 to 0.5.

In the airbag, the airbag device and the vehicle of the presentinvention, when the airbag is inflated, the left half airbag receivesthe left side of the occupant's thorax and the right half airbagreceives the right side of the occupant's thorax. The left and rightsides of the thorax have hard and strong rib bones. The airbag receivesand absorbs an impact on the occupant through the rib bones. In theinflated state, the airbag has the space between the distal ends of theleft and right half airbags, and the space faces a central portion ofthe occupant's thorax where a breastbone is situated. Accordingly, whenthe occupant's body plunges into the airbag, the portion around thebreastbone does not receive a strong impact, thereby decreasing a loadon the breastbone.

In the present invention, the distance between the distal ends of theleft half and right half airbags is set to be 150 to 450 mm when theairbag is inflated. As a result, the left half airbag faces a center ofthe left side of the thorax and the inflated right half airbag faces acenter of the right side of the thorax, thereby securely receiving theoccupant's upper body around the rib bones. Also, the distance from thedistal ends to the deepest bottom of the space is set to be 280 to 480mm, thereby decreasing a load on the breastbone.

In the present invention, a common inflator may be provided forinflating both the left half airbag and the right half airbag, therebyreducing the number of the inflators and a manufacturing cost.

In the present invention, the left half airbag is connected with theright half airbag at the middle portions of the surfaces facing eachother in a direction that the airbag deploys. When the airbag isinflated, a distance from the distal ends of the left and right halfairbags to the connected middle portions may be 50 to 300 mm. With sucha configuration, when one of the half airbags inflates later, the otherof the half airbags facilitates the one of the half airbags to beinflated by pulling the one of the half airbags. Also, the one of thehalf airbags starts to pull the other of the half airbags in thedirection of deployment at an early stage when the one of the half bagsis inflated up to the middle. Accordingly, both of the left and righthalf airbags are inflated smoothly and substantially uniformly towardleft and right sides from the early stage of the inflation. Further, theconnected portions are located at a deep position in the space betweenthe left and right half airbags, so that the joined portions do notapply a load on the breastbone.

In the present invention, the left and right half airbags are formed ofa plurality of the joined panels. The panels are joined at the joinedportions at an outside and the middle of the airbag in the direction ofdeployment. The joined portions at the middle of the opposing surfacesof the left and right half airbags may be connected. In this case, a tiepanel for connecting the left half airbag and the right half airbag isnot necessary, thereby reducing a cost of the airbag.

In the present invention, the vent holes are provided for discharginggas therethrough upon receiving the occupant, thereby absorbing theimpact on the occupant. The vent holes are formed in the outer sidesurfaces at the upper front areas from the middle portions of the sidesurfaces. When the airbag is inflated, the horizontal distance L1between the rear edge of the instrumental panel and the distal end ofthe airbag and the horizontal distance L2 between the rear edge of theinstrument panel and the vent hole has a ratio (L2/L1) of 0.25 to 0.5.Also, when the airbag is inflated, the vertical distance H1 between anupper edge of the instrumental panel and the upper edge of the airbagand the vertical distance H2 between the upper edge and the vent holehas a ratio (H2/H1) of 0.3 to 0.5. When the vent holes are located atthe relatively upper front areas, it is possible to securely prevent thedischarged gas through the vent holes from affecting the occupant.Further, when the ratio (L2/L1) is 0.25 to 0.5 and the ratio (H2/H1) is0.3 to 0.5, the vent holes do not closely contact an interior of thevehicle such as a door glass or A pillar, so that the gas is smoothlydischarged through the vent holes.

In the present invention, it is possible to protect the occupant evenwhen the airbag is inflated with a relatively low gas pressure. When theairbag is inflated with the maximum pressure less than, for example, 440kPa, it is still possible to protect the occupant. The vehicle providedwith the airbag may be further provided with a curtain airbag device, aknee airbag device, a knee protector or a seat cushion bag device toprotect the occupant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) are views showing an airbag according to anembodiment of the present invention, wherein FIG. 1( a) is a perspectiveview of the airbag in an inflated state, and FIG. 1( b) is a sectionalview taken along line 1(b)—1(b) in FIG. 1( a);

FIG. 2 is a sectional view taken along line 2—2 in FIG. 1( b);

FIG. 3( a) is an exploded perspective view of the airbag shown in FIG.1( a), and FIG. 3( b) is an enlarged view of a part 3(b) of the airbagshown in FIG. 1( a);

FIG. 4 is a view showing an airbag according to another embodiment ofthe present invention;

FIG. 5 is a view showing an airbag according to a further embodiment ofthe present invention;

FIG. 6 is a side view showing an airbag having a vent hole; and

FIG. 7 is a side view showing a vehicle provided with various airbagdevices.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be described withreference to the accompanying drawings. FIG. 1( a) is a perspective viewof an inflated airbag according to an embodiment of the presentinvention, and FIG. 1( b) is a sectional view taken along line 1(b)—1(b)in FIG. 1( a). FIG. 2 is a sectional view taken along line 2—2 in FIG.1( b). FIG. 3( a) is an exploded perspective view of the airbag, andFIG. 3( b) is an enlarged view of a portion 3(b) in FIG. 3( a).

An airbag 10 includes a right half airbag 12 to be inflated at a frontright of a vehicle occupant, a left half airbag 14 to be inflated at afront left of the occupant, and a communicating portion 16 forcommunicating an end of the right half airbag 12 with an end of the lefthalf airbag 14. The communicating portion 16 is located at a side of abase of the airbag 10. Accordingly, the right half airbag 12 and theleft half airbag 14 are inflated toward a direction that the halfairbags move away from the communicating portion 16.

In the inflated state of the airbag 10, a bridge component such as a tiepanel is not disposed between the distal ends of the right half airbag12 and the left half airbag 14. A space 13 between the distal ends ofthe right half airbag 12 and the left half airbag 14 is open toward theoccupant (i.e. upward in FIG. 1( b)). A distance W between a distal end12 t of the right half airbag 12 and a distal end 14 t of the left halfairbag 14 preferably ranges from 150 to 450 mm, and more preferablyranges from 170 to 430 mm. A horizontal distance A between the distalends 12 t and 14 t and the deepest bottom of the space 13 preferablyranges from 280 to 480 mm, and more preferably ranges from 310 to 450mm.

In the airbag 10, the right half airbag 12 is connected with the lefthalf airbag 14 with seams 52 at midsections thereof in a direction thatthe airbag is inflated. A horizontal distance B between the distal ends12 t and 14 t and the seams 52 is preferably ranges from 50 to 300 mm,and more preferably ranges from 90 to 260 mm.

According to the embodiment, the airbag 10 is composed of panels 18, 20,22, 24, 26, and 28, and the panels are stitched together. The panels 26and 28 are provided with vent holes 26 a and 28 a (26 a is not shown),respectively. As shown in FIG. 1( a), the vent holes 26 a and 28 a areformed in side surfaces of the airbags 12 and 14 facing outwardly. Thevent hole 26 a formed in the panel 26 (not shown) is located at aposition symmetrical to that of the vent hole 28 a.

A configuration of the panels will be described next in detail. As shownin FIG. 3( a), the panel 18 (rear inner panel) constitutes rear innersurfaces of the right half airbag 12 and left half airbag 14 from themidsections in the direction of inflation, and an inner central surfaceof the communicating portion 16. The panel 20 (rear outer panel)constitutes a surface (outer surface of the airbag) opposite to the rearinner panel 18.

The panels 22 and 24 (front inner panels) constitute front innersurfaces of the right half airbag 12 and the left half airbag 14 fromthe midsections in the direction of inflation (opposing surfaces of theright half airbag 12 and the left half airbag 14). The panels 26 and 28(front outer panels) constitute front outer surfaces (outer faces of theairbag) opposite to the front inner panels 22 and 24.

The rear inner panel 18 and the rear outer panel 20 are stitched withseams 30 (stitching threads). The rear inner panel 18 and the frontinner panel 22 are stitched with a seam 32. The rear inner panel 18 andthe front inner panel 24 are stitched with a seam 34. The rear outerpanel 20 and the front outer panel 26 are stitched with a seam 36. Therear outer panel 20 and the front outer panel 28 are stitched with aseam 38.

A vent hole 28 a for the left half airbag is disposed in the front outerpanel 28. Although not shown in the drawings, a similar vent hole forthe right half airbag is disposed in the front outer panel 26.

As shown in FIG. 1( a), seam allowances (joint portions) 44 and 46connect the rear inner panel 18 and the front inner panel 22, and therear inner panel 18 and the front inner panel 24, respectively, and areexposed at an outside of the right half airbag 12 and the left halfairbag 14. As shown FIGS. 1( a) and 2, tongue-shaped seam allowances 48and 50 protrude from the seam allowances 44 and 46 (FIG. 2 shows onlythe seam allowance 48). As shown in FIGS. 1( a) and 1(b), in particularin FIG. 1( b), the seam allowances 48 and 50 are stitched with seams 52.

As described above, the opposing surfaces of the right half airbag 12and the left half airbag 14 are connected at the midsections thereof inthe direction of inflation at the seam allowances 44, 46 of the rearinner panel 18 and the front inner panels 22, 24. A distance between arear end 10 e of the inflated airbag and the seams 52 preferably rangesfrom 30% to 70% of a longitudinal length L of the inflated airbag 10,and more preferably ranges from 40% to 55% of the length L.

A pair of slits 54 for inserting an inflator is formed in the rear outerpanel 20 constituting the outer surface of the communicating portion 16.As shown in FIGS. 1( a) and 1(b), a rod inflator 56 is used in thepresent embodiment. The rod inflator 56 is inserted into the slits 54such that the inflator 56 extends through the communicating portion 16in the width direction of the vehicle. Both ends of the inflator 56 aredisposed outside of the airbag 10.

The airbag 10 is installed in an airbag device for protecting a vehicleoccupant in the event of vehicle collision. The airbag device includes,for example, a box case with no lid (not shown) for accommodating theairbag 10, and the airbag 10 is connected with the case. As shown inFIG. 1( b), holes 58 are formed in the airbag 10 for inserting afastener (not shown) such as a bolt to fix the airbag 10 to the case.Both ends of the inflator 56 are also attached to the case.

The airbag 10 is folded in the case and a cover such as a lid (notshown) is mounted on the case to cover the folded airbag 10, thuscomposing the airbag device. The lid is adapted to be torn by a pressingforce exerted by the airbag 10 when the airbag is inflated.

The airbag device is installed in, for example, an instrument paneldisposed in front of a passenger seat of a vehicle. In the event ofvehicle collision, the inflator 56 ejects gas to the communicatingportion 16. The gas from the inflator 56 flows in the right half airbag12 and the left half airbag 14, thereby inflating the right half airbag12 toward the front right of the occupant and the left half airbag 14toward the front left of the occupant.

According to the airbag 10, the right half airbag 12 and the left halfairbag 14 are inflated from the folded state. Furthermore, the righthalf airbag 12 and the left half airbag 14 are connected. When one ofthe half airbags 12 and 14 is inflated faster and the other of the halfairbags 14 and 12 is inflated slower, the one half airbag facilitatesthe other half airbag to be inflated by pulling the other half airbag.As described above, the right half airbag 12 is connected to the lefthalf airbag 14 with the seams 52 at the midsections thereof in thedirection of inflation. Therefore, the one half airbag starts to pullthe other half airbag from an early stage of inflation. Accordingly,both of the right half airbag 12 and the left half airbag 14 areinflated smoothly and substantially uniformly toward the left and rightsides from the early stage of inflation.

In the completely inflated state of the airbag 10, the space 13 isformed between the distal ends of the right half airbag 12 and the lefthalf airbag 14, and the space 13 is open toward the occupant. Theinflated right half airbag 12 receives the right side of the occupant'sthorax, the left half airbag 14 receives the left side of the occupant'sthorax, and a portion around the occupant's breastbone faces the space13. Therefore, when the occupant plunges into the airbag, a forceapplied to the portion around the breastbone is decreased. When theairbag receives the occupant, gas in the airbag 10 is discharged throughthe vent holes 26 a and 28 a, thereby absorbing an impact.

A process of manufacturing the airbag 10 will be explained next. Asshown in FIG. 3( a), the rear inner panel 18 and the front inner panel22 are stitched with the seam 32, and the rear inner panel 18 and thefront inner panel 24 are stitched with the seam 34 (FIG. 3( a) does notshow the seam 34). The rear outer panel 20 and the front outer panel 26are stitched with the seam 36, and the rear outer panel 20 and the frontouter panel 28 are stitched with the seam 38 (FIG. 3( a) doe not showthe seam 38). The seam allowances 44 and 46 connecting the rear innerpanel 18 and the front inner panels 22 and 24 are disposed at theoutside of the airbag in the finished state as the airbag device.

In the present embodiment, the seam allowance 44 connects the rear innerpanel 18 and the front inner panel 22. As shown in FIG. 3( b), the rearinner panel 18 and the front inner panel 22 are stitched with the seam32 (32 a and 32 b) only at both ends of the seam allowance 44. Anopening 60 for reversing the airbag is formed between the seam 32 a andthe seam 32 b.

The rear inner panel 18 stitched with the front inner panels 22 and 24,and the rear outer panel 20 stitched with the front outer panels 26 and28 are overlapped such that outer surfaces of the airbag product faceeach other. The two stitched components are stitched with the seams 30,40, and 42 at the peripheries thereof so that an intermediate airbagproduct is obtained in a reversed state.

The intermediate airbag product is reversed through the opening 60formed in the seam allowance 44. The joint allowances 48 and 50 of theseam allowances 44 and 46 are stitched with the seams 52, therebycompleting the airbag 10 product. When the joint allowances 48 and 50are stitched, the seams 52 close the opening 60.

As descried above, the airbag 10 is composed of a plurality of thepanels. Accordingly, it is possible to form the outer surface of theairbag 10 having a large area and a complicated shape by the relativelysmall panels.

In the present embodiment, the seam allowances 44 and 46 connecting therear inner panel 18 and the front inner panels 22 and 24 are joined, sothat the right half airbag 12 is connected to the left half airbag 14.Therefore, it is not necessary to provide a tie panel for connecting theright half airbag 12 and the left half airbag 14 in addition to thepanels 18, 22 and 24, thereby reducing a cost of the airbag.

In the present embodiment, a pair of slits 54 used as openings for theinflator is disposed in the rear outer panel 20 constituting thecommunicating portion 16. The rod inflator 56 is inserted into the slits54, and disposed in the communicating portion 16. The slit openings forthe inflator provide superior connection strength of the inflator 56 tothe airbag 10.

In the manufacturing process of the airbag of the present embodiment,the opening 60 is provided in the seam allowance 44 for reversing theairbag product. Accordingly, in a case that it is difficult to reversethe intermediate airbag product through the vent hole or the opening ofthe inflator, in particular, in a case that the opening of the inflatoris composed of the slits as described above, it is easy to reverse theintermediate airbag product through the opening 60.

Incidentally, the seams 52 close the opening 60 when the joint allowance48 is stitched with the joint allowance 50. Therefore, the gas does notleak from the right half airbag 12 and the left half airbag 14 throughthe opening 60.

The embodiment described above is an example of the present invention,and the present invention is not limited to the embodiments illustratedin the drawings. For example, in the embodiment, the right half airbag12 and the left half airbag 14 are connected at the base side.Alternatively, the half airbags may be separated. More than twoinflators may be provided for inflating the right half airbag and theright half airbag separately. The midsections of the left half airbagand the right half airbag may be connected by a panel, a string, a netand the like. The left half airbag and the right half airbag may have asymmetric or asymmetric shape. The left half airbag and the right halfairbag may have the same capacity or different capacities.

In the present invention, as shown in FIG. 4, a section of the airbagdisposed at an A pillar side, i.e. a left half airbag 12A in FIG. 4, maybe arranged such that an upper part of the half airbag 12A is inclinedin a vehicle cabin, so that the half airbag does not contact the Apillar, a windshield, and a side window.

As shown in FIG. 5, the half airbags may have shapes such that thewidths gradually decrease toward the upper parts.

When the airbag of the invention is inflated with a relatively low gaspressure, it is still possible to securely protect the occupant. Inparticular, when the left and right half airbags have a capacity of morethan 45 liter, preferably more than 50 liter, more preferably more than65 liter, respectively, it is possible to securely protect the occupanteven with a low gas pressure. In this case, the inflator may have anoutput pressure of less than 430 kPa when measured for the inflatoritself (tank pressure for 60 liter), less than 400 kPa in some cases, orless than 350 kPa in a specific case. The gas pressure or inner pressurefor inflating the airbag may be more than 310 kPa, preferably 360 kPa.

When the airbag of the invention is inflated with a low gas pressure, itis possible to protect the occupant with a constant gas pressureregardless of a weight of the occupant or a speed of the vehicle upon acollision. In a conventional passenger airbag, it is necessary toincrease the gas pressure when a weight of the occupant is large or aspeed of the vehicle is high upon a collision. In the airbag of thepresent invention, it is possible to protect the occupant with aconstant gas pressure regardless of a weight of the occupant or a speedof the vehicle upon a collision, thereby reducing a cost of the airbagsystem.

It may be arranged that the inflator is not activated upon a collisionwhen the occupant is an infant. Also, it may be arranged that theinflator is not activated upon a collision when a child seat is mountedon a seat backward. In the present invention, it is possible to installan inflator with multi-step output or a plurality of inflators toregulate the gas pressure according to a weight of the occupant or aspeed of the vehicle upon a collision.

In FIG. 6, a passenger airbag device is provided with the airbag of theinvention having vent holes 26 a and 28 a at appropriate locations (inFIG. 6, a vent hole 26 a is not shown). As shown in FIG. 6, thepassenger airbag device is installed on an upper surface of aninstrumental panel 70 facing upwardly. The airbag 10 is retained in acontainer (not shown) in a folded state, and a lid covers a frontopening of the container. The lid may be a part of the instrumentalpanel, or a separate member.

When the airbag 10 is fully inflated, the vent holes 26 a and 28 a arelocated in the side surfaces of the airbags 12 and 14 at the areassubstantially around the centers thereof or upper front of the centers.

In particular, when a distance L1 is between a rear edge 71 of theinstrumental panel (the further most point of the surface of theinstrumental panel toward the rear side of the vehicle) and a rear endof the airbag 10 and a distance L2 is between the rear edge 71 of theinstrumental panel and centers of the vent holes 26 a and 28 a, the ventholes are located at the most preferable positions at a ratio L2/L1 of0.25 to 0.50, more preferably 0.26 to 0.45. When a vertical distance H1is between an upper edge 72 of the instrumental panel (the upper mostpoint of the surface of the instrumental panel around the airbag device,i.e. closest to a windshield of the vehicle) and an upper end of theairbag 10 and a vertical distance H2 is between the upper edge 72 of theinstrumental panel and the centers of the vent holes 26 a and 28 a, thevent holes are located at the most preferable positions at a ratio H2/H1of 0.3 to 0.50, more preferably 0.32 to 0.40.

When the vent holes 26 a and 28 a are located at the most preferablepositions, it is possible to prevent the gas discharging through thevent holes 26 a and 28 a from blowing against the occupant. It is alsopossible to prevent the vent holes 26 a and 28 a from closely contactinga surface of a vehicle member such as a side window, an A pillar and thewindshield 73. Accordingly, the gas is smoothly discharged through thevent holes 26 a and 28 a.

The vehicle provided with the airbag device of the invention may beprovided with other airbag devices such as a knee airbag device or aknee protector. FIG. 7 is a longitudinal sectional view showing anexample of such a vehicle. The passenger airbag device having thepassenger airbag 10 of the invention is mounted on the upper surface ofthe instrumental panel 70. A knee airbag device 80 is mounted under theinstrumental panel 70. In this embodiment, a case 82 for a knee airbagis installed in the instrumental panel 70. A knee bag 84 is retained inthe case 82 in a folded state and is fixed to the case 82 with afastener. An inflator (gas generator) 88 is installed in the case 82 forinflating the knee airbag 84. The case 82 has an opening along theinstrumental panel 70, and a lid covers the opening.

When the vehicle is collided, the inflator 88 ejects gas to inflate theknee airbag 84. The inflating knee airbag 84 pushes the lid to open, andthe knee airbag 84 is expanded along a front surface of the case 82 andthe surrounding instrumental panel 70. The knee airbag receives the legsof the occupant for protection.

In this embodiment, when the knee airbag 84 and the airbag 10 are fullyinflated (in a case of no occupant), an upper end of the knee airbag 84is located slightly above a lower end of the airbag 10. The vehicle isfurther provided with a curtain airbag device 90, a side airbag device100 and a seat cushion bag device 100. The curtain airbag device 90includes a curtain airbag 94 extending from an A pillar 91 to a C pillar93 above a B pillar 92, and an inflator 95 for inflating the curtainairbag 94. The curtain airbag 94 is disposed in a long folded state fromthe A pillar 91 to the C pillar 93 through a roof side portion 96, andis covered with a pillar garnish and a rood trim.

When the vehicle is collided or rolled over and the inflator isactivated, the curtain airbag 94 pushes the pillar garnish and the roodtrim and is deployed in the vehicle cabin downwardly along the pillars91, 92, and 93 and a side door. The expanded curtain airbag 94 receivesthe occupant to absorb an impact or to prevent the occupant fromejecting out of the vehicle.

The side airbag device 100 is installed in a seatback 101. The sideairbag device 100 includes a side airbag 103 retained in a case 102 in afolded state and an inflator 104 for inflating the aide airbag 103. Whenthe vehicle is collided or rolled over and the inflator 104 isactivated, the side airbag 103 breaks a seatback cover and is expandedat an upper side of the occupant at a side of the door to protect theoccupant. The side airbag device may be installed at a location such asa side door other than the seatback.

The seat cushion bag device 110 includes a seat cushion bag 112 disposedinside a front portion or under a lower portion of a seat cushion 111,and an inflator (not shown) for inflating the seat cushion bag. When thevehicle is collided and the inflator is activated, the seat cushion bagis inflated and pushes the seat cushion 111 upwardly. Accordingly, thefront portion of the seat cushion 111 is pushed upwardly or is hardened.As a result, it is possible to prevent the occupant from moving forward.Reference numeral 106 denotes a seat belt (lap belt).

As described above, according to the present invention, the airbag andthe airbag device include the left half airbag for receiving the leftside of the occupant's thorax, the right half airbag for receiving theright side of the occupant's thorax, and the space disposed between thetwo half airbags to face the portion around a breastbone of theoccupant. In the airbag and the airbag device, both of the left halfairbag and the right half airbag are inflated smoothly and substantiallyuniformly toward the left and right sides from the early stage ofinflation.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

1. An airbag for protecting an occupant, comprising: a left half airbagto be inflated at a front left of the occupant and having a distal endand a vertically curved surface projecting toward the occupant in amiddle portion thereof when inflated, and a right half airbag to beinflated at a front right of the occupant and having a distal end and avertically curved surface projecting toward the occupant in a middleportion thereof when inflated, said distal ends of the left and righthalf airbags being unconnected and separated from each other to form aspace therebetween facing the occupant when the airbag is inflated. 2.An airbag according to claim 1, wherein said distal ends of the left andright half airbags are spaced apart from each other by a distancebetween 150 and 450 mm, and are located away from a deepest bottom ofthe space by 280 to 480 mm in a horizontal direction when the airbag isinflated.
 3. An airbag according to claim 1, further comprising a basefor communicating the left and right half airbags, said left and righthalf airbags being inflatable by a common inflator.
 4. An airbagaccording to claim 1, wherein said left half airbag is connected withthe right half airbag at midsections thereof so that the distal ends ofthe left and right half airbags are located away from the midsections by50 to 300 mm in a horizontal direction when the airbag is inflated. 5.An airbag according to claim 4, wherein each of said left half airbagand said right half airbag is formed of a plurality of panels havingjoint allowances disposed at the midsection, said left half airbag beingconnected with the right half airbag at the joint allowances.
 6. Anairbag according to claim 1, wherein at least one of said left halfairbag and said right half airbag has an inclined upper portion when theairbag is inflated.
 7. An airbag according to claim 1, wherein at leastone of said left half airbag and said right half airbag has a widthgradually decreasing upwardly when the airbag is inflated.
 8. An airbagfor protecting an occupant, comprising: a left half airbag to beinflated at a front left of the occupant and having a distal end and avertically curved surface projecting toward the occupant in a middleportion thereof when inflated, and a right half airbag to be inflated ata front right of the occupant and having a distal end and a verticallycurved surface projecting toward the occupant in a middle portionthereof when inflated, said distal ends of the left and right halfairbags being unconnected and separated from each other to form a spacetherebetween facing the occupant when the airbag is inflated, whereineach of said left and right half airbags has a vent hole formed at aside surface thereof at a position around a center of the side surfaceor upper front of the center.
 9. An airbag device comprising the airbagaccording to claim 1 and an inflator for inflating the airbag.
 10. Anairbag device according to claim 9, wherein said airbag is inflated at agas pressure less than 440 kPa.
 11. A vehicle provided with the airbagdevice according to claim
 9. 12. A vehicle provided with an airbagdevice comprising an airbag and an inflator for inflating the airbag,said airbag comprising: a left half airbag to be inflated at a frontleft of the occupant and having a distal end and a vertically curvedsurface projecting toward the occupant in a middle portion thereof wheninflated , and a right half airbag to be inflated at a front right ofthe occupant and having a distal end and a vertically curved surfaceprojecting toward the occupant in a middle portion thereof wheninflated, said distal ends of the left and right half airbags beingunconnected and separated from each other to form a space therebetweenfacing the occupant when the airbag is inflated, wherein said airbagdevice is installed in an instrumental panel of the vehicle, and saidairbag is a passenger airbag having vent holes in side surfaces thereoffacing outwardly so that a ratio L2/L1 of a horizontal distance L1between a rear edge of the instrumental panel and the distal ends of theleft and right half airbags to a horizontal distance L2 between the rearedge of the instrumental panel and the vent holes is between 0.25 to0.50.
 13. A vehicle provided with an airbag device comprising an airbagand an inflator for inflating the airbag, said airbag comprising: a lefthalf airbag to be inflated at a front left of the occupant and having adistal end and a vertically curved surface projecting toward theoccupant in a middle portion thereof when inflated, and a right halfairbag to be inflated at a front right of the occupant and having adistal end and a vertically curved surface projecting toward theoccupant in a middle portion thereof when inflated, said distal ends ofthe left and right half airbags being unconnected and separated fromeach other to form a space therebetween facing the occupant when theairbag is inflated, wherein said airbag device is installed in aninstrumental panel of the vehicle, and said airbag is a passenger airbaghaving vent holes in side surfaces thereof facing outwardly so that aratio H2/H1 of a vertical distance H1 between an upper edge of theinstrumental panel and an upper end of the airbag to a vertical distancebetween the upper edge of the instrumental panel and the vent holes isbetween 0.3 to 0.50.
 14. A vehicle according to claim 11, furthercomprising at least one of a curtain airbag device, a knee airbagdevice, a knee protector, a side airbag device and a seat cushion bagdevice.
 15. An airbag according to claim 1, wherein each of saidvertically curved surfaces of said left and right half airbags has upperand lower portions with respect to the middle portion, respectively, andprojects from the upper and lower portions to the middle portion closeto a body of the occupant.